It could be so many things. One likely thing is that you're finally in a place where you can rest, after a period of high stress. Then, all the tiredness that was being pent up, comes crashing down.
Surgery for skin cancer? That sounds like it could make you pretty sleepy for a while. Sleep helps you recover.
If you're worried and it continues, it's always best to check it out with a doctor.
Well done for getting through the last couple of months
---------- Post added at 01:16 ---------- Previous post was at 01:10 ----------
Oh PS I've experienced being suicidal, intimately. It did scare me to be suicidal. Being suicidal and being scared of being suicidal are two different things. They can exist at the same time, or just one, or just the other, or neither.
Feeling suicidal is different from just wanting to be asleep for a long time. That is certainly a thought I had sometimes - just to check out of life - but it's more than just that. It's total incredible agony, violent and loud and horrible. It's like listening to terrifically loud head-splitting screeching, when everyone else seems to be hearing music, and you just want to turn it off. It's a desire to escape the vast hellish pain. It doesn't sound like you're experiencing that kind of desperate agony.